Proceedings of the Zoological Institute RAS Vol. 314, No. 1, 2010, рр. 24–41 УДК 598.132.6:568.132 ITILOCHELYS RASSTRIGIN GEN. ET SP. NOV, A NEW HARD-SHELLED SEA TURTLE (CHELONIIDAE SENSU LATO) FROM THE LOWER PALEOCENE OF VOLGOGRAD PROVINCE, RUSSIA I.G. Danilov1*, A.O. Averianov1 and A.A. Yarkov2 1Zoological Institute of the Russian Academy of Sciences, Universitetskaya Emb. 1, 199034 Saint Petersburg, Russia; e-mails: [email protected]; [email protected] 2Museum of Natural History, Humanitarian Institute, 40 Let Pobedy Str., 404132 Volzhskii, Volgograd Province, Russia; e-mail: [email protected] ABSTRACT Itilochelys rasstrigin, gen. et sp. nov., a new hard-shelled sea turtle (Cheloniidae sensu lato), is established based on a partial skull, two lower jaws, a humeral bone and cervical vertebrae I–III from the Lower Paleocene of Volgograd Province, Russia. Itilochelys rasstrigin differs from other cheloniids s.l. by the following combination of characters: (1) long skull; (2) short snout; (3) deep cheek emargination; (4) frontal contributing to orbital margin; (5) prefrontal/ postorbital contact absent; (6) long anteroventral process of postorbital; (7) extensive secondary palate; (8) moderate vomer length on triturating surface; (9) deep and narrow midline groove on triturating surface through vomer length; (10) swellings lateral to midline groove present; (11) long lower jaw symphysis; (12) concave lower triturating surface; (13) blunt and shallow symphyseal ridge ending in a triangular elevation; (14) lingual ridges on the lower jaw absent. The new taxon increases diversity of stem-cheloniids and represents the most complete finding of these turtles in Russia. Key words: Cheloniidae, Paleocene, Russia, Testudines, Volgograd Province ITILOCHELYS RASSTRIGIN GEN. ET SP. NOV, НОВАЯ ТВЕРДОПАНЦИРНАЯ МОРСКАЯ ЧЕРЕПАХА (CHELONIIDAE SENSU LATO) ИЗ НИЖНЕГО ПАЛЕОЦЕНА ВОЛГОГРАДСКОЙ ОБЛАСТИ, РОССИЯ И.Г. Данилов1*, А.O. Аверьянов1 и A.A. Ярков2 1Зоологический институт Российской академии наук, Университетская наб. 1, 199034 Санкт-Петербург, Россия; e-mails: [email protected]; [email protected] 2Историко-краеведческий музей, Волжский гуманитарный институт, ул. 40 лет Победы, 404132 Волжский, Волгоградская область, Россия; e-mail: [email protected] РЕЗЮМЕ Itilochelys rasstrigin gen. et sp. nov., новая твердопанцирная морская черепаха (Cheloniidae sensu lato), установ- лена на основе неполного черепа, двух нижних челюстей, плечевой кости и I–III шейных позвонков из ниж- него палеоцена Волгоградской области, Россия. Itilochelys rasstrigin отличается от других хелониид следую- щей комбинацией признаков: (1) длинный череп; (2) короткое рыло; (3) глубокая нижняя височная вырезка; (4) участие лобных костей в формировании краев глазниц; (5) контакт предлобной/заглазничной костей отсутствует; (6) длинный антеровентральный отросток заглазничной кости; (7) хорошо развитое вторичное костное нёбо; (8) сошник умеренной длины на альвеолярной поверхности; (9) глубокий и узкий средин- *Corresponding author / Автор-корреспондент. A new cheloniid turtle from the Paleocene of Russia 25 ный желоб на альвеолярной поверхности вдоль всей длины сошника; (10) вздутия по бокам от срединного желоба имеются; (11) длинный нижнечелюстной симфиз; (12) вогнутая альвеолярная поверхность нижней челюсти; (13) тупой и низкий симфизный гребень, оканчивающийся треугольным возвышением; (14) линг- вальные гребни нижней челюсти отсутствуют. Новый таксон увеличивает разнообразие стволовых хелони- ид и представляет наиболее полную находку этих черепах в России. Ключевые слова: Cheloniidae, палеоцен, Россия, Testudines, Волгоградская область INTRODUCTION MATERIAL Cretaceous and Paleogene turtles of European In addition to the materials described in this pa- Russia are poorly known. They are represented by re- per, the following taxa of stem-cheloniids were used mains of various sea turtles (Chelonioidea), soft shell for comparison: “Argillochelys” africana Tong and turtles (Trionychidae; beginning with Paleocene) Hirayama, 2008, as described by Tong and Hirayama and undetermined turtle material (Averianov and (2008), we consider this taxon as separate from Yarkov 2000, 2004; Averianov 2002). Most of these typical Argillochelys Lydekker, 1889, due to many remains come from several Late Cretaceous and Pa- differences from the latter and until its relationships leocene localities in Volgograd Province (Averianov is shown by phylogenetic analysis (see Discussion); and Yarkov 2000, 2004). Usually these materials are Argillochelys cuneiceps (Owen, 1849) (type species of very fragmentary and allow only family level deter- Argillochelys), as described by Owen and Bell (1849) minations. In this paper we describe more complete and personal observations (IGD) of BMNH 41636, turtle specimens, including a partial skull and other the holotype, based on photos offered by Ren Hi- remains of a hard-shelled sea turtle (Cheloniidae sen- rayama; Eochelone brabantica Dollo, 1903 (type spe- su lato), from the lower Paleocene (Danian) deposits cies of Eochelone Dollo, 1903), as described by Casier of Rasstrigin locality (= Rasstrigin 2), Dubovka (1968); Euclastes hutchisoni Lynch and Parham, District, Volgograd Province, Russia (Fig. 1). This 2003 (one of the better-known species of Euclastes material is attributed to a new genus and species – It- Cope, 1867; Lynch and Parham 2003), as described ilochelys rasstrigin gen. et sp. nov. We follow a phylo- by Lynch and Parham (2003); Puppigerus camperi genetic taxonomy and use Cheloniidae sensu lato for Gray, 1831 (type species of Puppigerus Cope, 1871), the stem-based definition of Cheloniidae and Chelo- as described by Moody (1974); Tasbacka aldabergeni niidae sensu stricto for the crown-group name (Lynch Nessov, 1987 (type species of Tasbacka Nessov, 1987), and Parham 2003; Joyce et al. 2004). Stem-cheloniids as described by Nessov (1987) and personal observa- include mostly Cretaceous and Paleogene forms with tions of CCMGE 1/12175, the holotype, by IGD. primitive morphology (see Parham and Fastovsky 1997). There are only two stem-cheloniids previously SYSTEMATICS reported from Russia. Both of them come from the late Paleocene of Volgograd Province and are based on very fragmentary remains: Euclastes sp. from Kar- Testudines Batsch, 1788 povka (= Bereslavka 2a) locality and cf. Tasbacka sp. Cryptodira Cope, 1868 from Malaya Ivanovka locality (Nessov and Yarkov Chelonioidea Baur, 1893 1989; Averianov and Yarkov 2000; Averianov 2002; Cheloniidae Bonaparte, 1832 sensu lato Lynch and Parham 2003). Thus, Itilochelys rasstrigin not only increases diversity of stem-cheloniids, but Itilochelys rasstrigin gen. et sp. nov. also represents the most complete finding of these (Figs. 2–11) turtles in Russia. Institutional abbbreviations. BMNH, Natural Etymology. The genus name is after Itil’, the History Museum, London, Great Britain; CCMGE, medieval Arabian/Persian name of Volga River; and Chernyshev’s Central Museum of Geological Explo- χέλυς, the Greek word for turtle. The species name is ration, St. Petersburg, Russia; ZIN PH, Paleoherpeto- after Rasstrigin locality. logical collection, Zoological Institute of the Russian Holotype. ZIN PH 1/118, partial skull with a dis- Academy of Sciences, Saint Petersburg, Russia. articulated lower jaw and I–III cervical vertebrae. 26 I.G. Danilov et al. Fig. 1. Locality and geology data of Rasstrigin locality: A – map of Rus- sia with Volgograd Province filled with black; B – map of Volgograd Province with Rasstrigin khutor shown by asterisk; C – schematic stratigraphic section in the Krutoi ravine, Rasstrigin 2 locality: a – sandstone; b – sand; c – remains of mosasaurs in the layer with dispersed phosphorites; d – phosphorites on the weathered horizon; e – crocodile vertebra; f – turtle remains. Referred material. ZIN PH 2/118, dentary; ZIN row snout. The ratio of its width (at the jugals) to PH 3/118, right humerus. All material was collected estimated length (from tip of the snout to the occipi- by the one of us (AAY) in 1990. tal condyle) is about 0.84. Thus, the skull is relatively Locality, horizon, and age. Rasstrigin 2 locality, longer than in Argillochelys cuneiceps (the same ratio middle of Krutoi ravine, 1 km North-West of Rasstri- is about 0.93) and Euclastes hutchisoni (1.05), but gin khutor, about 80 km North-North-West of Volgo- shorter than in Puppigerus camperi (0.60), Eochelone grad, Dubovka District, Volgograd Province, Russia; brabantica and Tasbacka aldabergeni (both – 0.78). the upper fossiliferous level, lower Paleocene, Danian The skull is high, as in living cheloniids, and thus (Averianov and Yarkov 2004). different from the much lower skull of Euclastes spp. Diagnosis. Can be differentiated from other che- The orbits are large and laterally directed as in most loniids s.l. by the following combination of characters: cheloniids, except some Euclastes (see Lynch and Par- (1) long skull; (2) short snout; (3) deep cheek emar- ham, 2003). The snout (preorbital part of the skull) gination; (4) frontal contributing to orbital margin; is relatively short making up about 20% of the skull (5) prefrontal/postorbital contact absent; (6) long length, similar to Argillochelys cuneiceps, but shorter and narrow anteroventral process of postorbital; than in other cheloniids s.l. used for comparison. The (7) extensive secondary palate; (8) moderate vomer apertura narium externa is oval-shaped and directed length on triturating surface; (9) deep and narrow anterodorsally. The skull is well roofed, with a shal- midline groove on triturating surface through vomer low temporal emargination. The cheek emargination, length; (10) swellings lateral to midline groove pres- as reconstructed, is rather deep, similar to “Argillo- ent; (11) long lower jaw symphysis; (12) concave chelys” africana. lower triturating surface; (13) blunt and shallow In palatal view, the secondary palate is extensive; symphyseal ridge ending in a triangular elevation; its maximal length makes up about 60% of the skull (14) lingual ridges on the lower jaw absent. length, similar to Puppigerus camperi and Tasbacka Description and comparisons. The skull has a aldabergeni, unlike Argillochelys cuneiceps and Eu- roughly triangular outline in dorsal view, with a nar- clastes hutchisoni, which have less developed (moder- A new cheloniid turtle from the Paleocene of Russia 27 Fig. 2. Skull of Itilochelys rasstrigin gen. et sp. nov., ZIN PH 1/118 (holotype), photos: A – dorsal view; B – ventral view; C – left lateral view; D – right lateral view. 28 I.G. Danilov et al. ate) secondary palate (45–50% of the skull length), the postorbital posterolaterally by a short suture. The and Eochelone brabantica, in which the secondary frontal makes a short contribution to the orbital mar- palate is absent. gin preventing the prefrontal/postorbital contact. Only parts of scale sulci are visible, but neverthe- The parietals are not complete, their dorsal plates less allow discerning supraorbital, temporal, parietal, are not connected with the the inferior parietal jugal and maxilla scales. The scale pattern of the processes. The parietal is the largest element of the middle part of the skull roof (i.e. presence and num- skull roof, forming the medial portion of the temporal ber of frontal, frontoparietal and additional scales) is emargination. It contacts the frontal anteriorly and not clear. the postorbital laterally by a very long suture. There The snout area of the skull, although somewhat is a small notch at the posterior border of the pari- damaged, shows that the nasal is clearly absent. Both etal, at point where the parietal is crossed with the prefrontals are well visible, although their contacts sulcus between parietal and temporal scales. Poste- with the maxillae are cracked on both sides. The rolaterally, the parietal has a short sutural surface for prefrontal is an anteroposteriorly elongated element contact with the squamosal, which is not preserved as seen from above, forming the upper rim of the in the described specimen. The processus inferior apertura narium externa and anterior portion of the parietalis has contacts (from front to back) with the upper margin of the orbit. The midline prefrontal/ pterygoid, prootic and supraoccipital. The foramen prefrontal contact makes up about one third of the nervi trigemini is well visible on the left side of the total prefrontal length, as also observed in Tasbacka braincase. It is a large oval-shaped opening bordered aldabergeni. The same contact is slightly longer in by the processus inferior parietalis anterodorsally, Argillochelys cuneiceps, Eochelone brabantica and prootic posteriorly and pterygoid ventrally. The pro- Euclastes hutchisoni and much longer in Puppigerus cessus inferior parietalis has short anterior extension camperi, making up about half of the total prefrontal to the lateral braincase wall similar to other Chelo- length. The prefrontal contacts the frontal postero- niidae sensu lato. medially and does not reach the postorbital posteri- Both postorbitals are preserved and complete. The orly, thus not separating the frontal from the orbital right postorbital is missing its anteroventral process, margin. This is similar to the condition in many che- whereas the left one has a little damage at the pos- loniids s.l., but unlike the condition in “Argillochelys” terior and medial borders. The postorbital is a large africana and Euclastes spp. and anteroposteriorly elongated flat bone, forming In the fossa orbitalis, the descending process of the posterodorsal portion of the orbital margin. Its the prefrontal contacts the palatine and the vomer proportions are similar to those of “Argillochelys” af- posteromedially and the maxilla laterally, although ricana, Eochelone brabantica, and Tasbacka aldaber- sutures between these bones are not always clear. geni, but different from those of Puppigerus camperi, The left frontal is complete, whereas the right one which has a much wider postorbital. The postorbital lacks its most posterior portion. The two frontals form contacts the frontal anteriorly at the orbital margin, a triangle as seen from above. The frontal contacts the the jugal anteroventrally, the quadratojugal poster- prefrontal by a strongly anteriorly convex suture, the oventrally and the parietal medially. Anteriorly, the parietal posteriorly by a straight transverse suture and postorbital forms a long and narrow anteroventral Fig. 3. Skull of Itilochelys rasstrigin gen. et sp. nov., ZIN PH 1/118 (holotype), drawings: A – dorsal view; B – ventral view; C – left lateral view; D – right lateral view; E – reconstruction of the ventral view of the skull (without scale). Bones are filled with light-grey (foreground) and dark-grey (background). Matrix is filled with black. Breakages are hatched. Abbreviations: ang – angular; art – articular; bo – basioccipital; bs – basisphenoid; btb – basis tuberculi basalis; cl – cavum labyrinthicum; co – condylus occipitalis; cor – coronoid; den – dentary; ds – dorsum sellae; exo – exoccipital; facci – foramen anterius canalis carotici interni; fcl – foramen caroticum laterale; fdm – foramen dentofaciale majus; fim – foramen intermandibularis medius; fm – fossa meckelii; fna – foramen nervi abducentis; fnh – foramen nervi hypoglossi; fnt – foramen nervi trigemini; fnv – foramen nervi vidiani; fon – foramen orbito-nasale; fpr – foramen praepalatinum; fr – frontal; foramen stapedio-temporalis; JU – jugal scale; ju – jugal; MX – maxilla scale; mx – maxilla; op – opisthotic; pa – parietal; PA – parietal scale; pal – palatine; pcl – processus clinoideus; pf – prefrontal; pm – premaxilla; po – postorbital; ppe – processus pterygoideus externus; pr – prootic; pra – prearticular; pt – pterygoid; qj – quadratojugal; qu – quadrate; rb – rostrum basisphenoidale; sc – sulcus cavernosus; scm – sulcus cartilaginis meckelii; so – supraoccipital; st – sella turcica; SU – su- praorbital scale; sur – surangular; TE – temporal scale; vo – vomer. A new cheloniid turtle from the Paleocene of Russia 29 30 I.G. Danilov et al. process, which considerably increases contribution tacts with the vomer is damaged. The suture between of the postorbital to the orbital margin. This process the premaxillae is visible only anteriorly and seems is much less developed in Argillochelys cuneiceps and to be obliterated posteriorly. The dorsal surface of the Tasbacka aldabergeni and absent in other cheloniids premaxilla bears a pair of anteroposteriorly directed used for comparison. Posteriorly, the postorbital has grooves. In ventral view, the premaxilla is wider a wide sutural surface for contact with the squamosal. anteriorly than posteriorly and nearly as long as the The postorbital does not reach the temporal emar- palatal portion of the vomer. gination, as in all cheloniids. There is a low, sharp Both maxillae are preserved, although their ante- and transversally directed ridge (transverse ridge) rior margins are damaged. In lateral view, the maxilla on the ventral surface of the postorbital, behind the contributes to the anterior and lower rim of the orbit orbit. It continues as a ridge on the jugal and extends and contacts the premaxilla anteriorly, the jugal pos- medially on the postorbital. It may have reached the teriorly and the prefrontal anterodorsally. In dorsal parietal as well, but this area is damaged in the de- view, the maxilla forms the lateral portion of the scribed specimen. A similar ridge is reported, among orbital floor, and contacts the palatine medially, the compared cheloniids, for “Argillochelys” africana, jugal posteriorly and the prefrontal anteromedially. Tasbacka aldabergeni and Euclastes hutchisoni. The foramen orbito-nasale is preserved on the left Both jugals, although damaged, allow reconstruct- side of the skull, but almost completely damaged on ing their shape. In lateral view, the jugal forms the the right side. It is formed by the maxilla laterally and posteroventral rim of the orbit and the anterior half the palatine medially and posteriorly. It is unclear if of the cheek emargination. It contacts the maxilla the prefrontal contributes to its anterior margin or anteriorly below the orbit, the postorbital dorsally, not. In ventral view, the maxilla forms most of the and the quadratojugal posteriorly. The posterior part triturating surface and its labial ridge. The secondary of the jugal’s free border is notched, forming the an- palate (maximal length) is extensive, about 60% of the terior border of the cheek emargination. This notch skull length, which is similar to those of Puppigerus is absent in other cheloniids used for comparison. In camperi and Tasbacka aldabergeni. The anterior mar- ventral view, the jugal makes a small contribution gin of the apertura narium interna is at about two to the posterior end of the triturating surface. The thirds of the total length of the triturating surface, internal surface of the jugal bears a strong ridge pos- which is similar to the condition in “Argillochelys” teroventral to the orbit, which is the continuation of africana and Euclastes hutchisoni, but different from the postorbital ridge (see above). Another blunt and those in other cheloniids used for comparison. The low ridge extends from the point much lower than apertura narium interna itself is relatively narrow the point where the jugal-postorbital ridge meets the and long in ventral view. The triturating surface is jugal/postorbital suture to the cheek emargination. smoothly curved with a distinct midline groove (see This condition is similar to Tasbacka aldabergeni and vomer) and a pair of blunt swellings. The swellings different from “Argillochelys” africana, where this are well preserved and mainly formed by the maxilla. low ridge begins at the mentioned point. They are anteroposteriorly elongated, start posterior Incomplete quadratojugals are preserved on to the maxilla/premaxilla suture and reach maxilla/ both sides of the skull and represented only by their jugal suture posteriorly. On the triturating surface, upper parts. The quadratojugal is a sheet of bone the maxilla contacts the premaxilla anteriorly, the anterodorsal to the quadrate. It forms the posterior vomer medially, the palatine posteromedially and the portion of the cheek margin and the anterior rim of jugal posteriorly. the cavum tympani. It contacts the jugal anteriorly The vomer is almost complete. It is an antero- and the postorbital dorsally. Other contacts of the posteriorly elongate element, which can be divided quadratojugal (with the squamosal and quadrate) are into two parts: a horizontal ventral sheet and a dorsal not preserved. sheet that are connected by a vertical vomerine pil- The squamosals are not preserved, although their lar. The ventral sheet forms the central portion of the contacts with the parietal and postorbital are clear. triturating surface and the anteriodorsal rim of the Both premaxillae are damaged and represented by apertura narium interna. It is hexagonal, longer than fragments. Their contacts with the maxillae are pre- wide and makes up about 1/2 of the midline length of served only partially, whereas the area of their con- the secondary palate. Similar proportions of the vomer A new cheloniid turtle from the Paleocene of Russia 31 Fig. 4. Skull of Itilochelys rasstrigin gen. et sp. nov., ZIN PH 1/118 (holotype), photos: A – anterior view; B – posterior view; C – posterior view (braincase removed); D – braincase in left lateral view; E – braincase in dorsal view; F – braincase in anterior view. 32 I.G. Danilov et al. Fig. 5. Skull of Itilochelys rasstrigin gen. et sp. nov., ZIN PH 1/118 (holotype), drawings: A – anterior view; B – posterior view; C – pos- terior view (braincase removed); D – braincase in left lateral view; E – braincase in dorsal view; F – braincase in anterior view. See Fig. 2 for designations and abbreviations. A new cheloniid turtle from the Paleocene of Russia 33 Fig. 6. Lower jaws of Itilochelys rasstrigin gen. et sp. nov., photos: A–F – ZIN PH 1/118 (holotype): A – dorsal view; B – right lateral view; C – ventral view; D – anterior view; E – left posterolateral view; F – posterior view (left posterior fragment removed); G–K – ZIN PH 2/118: G – dorsal view; H – right lateral view; I – ventral view; J – anterior view; K – posterior view.